WMOD00379

• Title: Potential Opportunities for Precipitation Augmentation in the Eastern Tennessee Valley
• Date: 2/1/1988
• Weather Modification - Doc Type: Report

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1.0 INTRODUCTION

1.1 Background

On December 3, 1986, Dr. Michael D. High, Director of the Division of Energy
Demonstrations and Technology, and Mr. Bevan W. Brown, Director of Air and Water
Resources of the TVA (Tennessee Valley Authority), visited Dr. Bernard A.
Silverman and Mr. John C. Lease of the DARR (Division of Atmospheric Resources
Research), USBR (U.S. Bureau of Reclamation), in Denver, Colorado. The purpose
of the visit was to explore the possibilities of a cooperative project betwe~n
the USBR and the TVA to investigate the feasibility of implementing a precipita-
tion enhancement program in the Tennessee Valley region. They stated that
increased precipitation would augment streamflow and reservoir storage which
could be highly beneficial during some periods.

It was decided to send DARR representatives to the offices of the TVA to further
explore requirements and possibilities with TVA personnel. Accordingly, Mr.
John C. Lease and Dr. Arlin B. Super met with several TVA managers and technical
personnel on January 20-22, 1987, in Knoxville, Tennessee.

The Knoxville meetings were very productive and clarified" several issues. The
recent 2-year drought in the TVA region caused s~vere problems in system opera-
tion. In particular, low streamflows markedly reduced hydroelectrical power
generation capacity (hydropower). The,shortfall required that other much more
expensive power' generating sources (e.g., coal-fired plants, combustion tur-
bines) be utilized to a greater than normal extent. This resulted in higher
costs to consumers and possibly greater air pollution. Other TVA system
problems caused by the drought included degradations in water quality and in
recreational uses due to seVere reservoir drawdown and low streamflows. While
the TVA usually has adequate water to meet basic needs, additional water would
often allow the overall system to be more nearly optimized and lower priority
needs to be met.

Discussions during the Knoxville meetings revealed that wintertime precipitation
augmentation would usually serve little purpose for the TVA. Reservoirs are
generally drawn down to their minimum levels by the end of December to provide
flood protection. The heaviest, widespread precipitation events with greatest
general flooding potential usually occur with winter storms (especially slow
moving lows). By mid-March reservoir filling begins and it is required that
summer levels be reached by mid-to-late May to adequately meet seasonal demands.
The March 15 - May 31 period is, therefore, most critical for adequate rainfall.

Another important result of the Knoxville meetings was the identification of the
four highest priority areas for rainfall augmentation. Together these encompass
most of the northeastern tip of Tennessee (generally east .of a north-south line
through Knoxville), as well as western North Carolina and the southwestern end
of Virginia. These areas, hereafter referred to as the eastern TVA region, con-
tain the highest elevation headwater regions of the streams that form the
Tennessee River. Additional rainfall in,these,watersheds could be used several
times during passage through the many reservoirs in the TVA system.

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